Upper Point of Profile Adjustment 



^ 'nitlol Profile 



ile Adjusted To Submergence, 2 

 \ Elevoted Water Surfoce 



Point of Profile 

 Closure 



Figure 1. Sketch of profile measurements required to predict shore adjustment 

 to a change in water level elevation. Providing there is no net 

 gain' or loss outside the control volume, constancy of profile shape 

 requires that the ultimate shore retreat x be equal to zX/Z. 



The change in water level elevation should persist at least long enough for 

 equilibrium to be reestablished. The time required to do so will depend on 

 the magnitude of the water level change and on the occurrence of storms which 

 provide the energy necessary for reshaping the shore. To be consistent with 

 the time frame in which other terms of the equation will be evaluated, the 

 mean water level surface is expected to remain at its new elevation for more 

 than 1 year. The new water surface elevation may refer to expected changes 

 resulting from proposed modification to the lake control plans, or it may 

 refer to a past change in lake level which could have resulted from natural 

 variations in the water supply, but whose effect remains to be determined. 



2. Height of the Responding Profile, Z. 



This term refers to the vertical relief of the active beach which extends 

 from the closure depth offshore to the top of the affected deposits on the 

 backshore. The profile closure depth, beyond which the bottom does not 

 respond to surface changes, depends on the local wave climate. Estimates of 

 closure depths, based on the relationship between published wave climates and 

 repetitive profiling on Lake Michigan (Hands, 1980), are tabulated in the 

 Appendix for all five Great Lakes. The average height of the affected back- 

 shore deposits above the initial water surface should be determined from field 

 measurements at the particular site of application. The sum of the closure 

 depth (taken from the App. ) and the average backshore height (determined from 

 field surveys) is an estimate of Z. 



